Replacing 'word' in a string

Question

Hi! I want to replace Strings in a String, but if the the substring which has to be replaced is not a word, then i don't want it to be replaced. Eg.: I want to replace Words for other strings, where words are not substring of other Words :)
Just want to ask if someone has made this before, and can help me out
cu
athalay

Answer 1

But, my original question wasn't this. I
want to replace words(string) for other strings in
sentences(string). I hope it's clearer. So for example
I have a sentence: This is an applepie. And if I want
to replace apple for pear, then do not replace this
sentence for pearpie, just remain it, because there's
no "apple" word in this sentence. I hope it's clearer.
My main problem is, that handling the First word of
the sentence. It easy to replace " "+word+" " for what
I want, but there are separatorchars like , . etc :)Search for the word you want to replace. Once you have found it, you will need to do a series of other checks...
1) is it at the beginning or end of the sentence? (then you need to look at the character before or after the word depending on location in entire String to see if it is whitespace or separator character)
2) is it surrounded by whitespace or separator characters on both sides? (get the surrounding characters and compare to a list of acceptable characters to make this a word, ie " ", ",", ";"...
Only replace words that pass the conditions (beginning of sentence and followed by whitespace or separator, end of sentence and preceeded by whitespace or separator, or middle of sentence and surrounded by whitespace or separators).